class Student():
    def __init__(self):
        self._score = 10000

    @property
    def score(self):
        return self._score

    @score.setter
    def score(self, value):
        if value < 0:
            print(11111)
            return
        self._score = value

    @score.deleter
    def score(self):
        del self._score


a = Student()
del a.score
a.score = 10
print(a.score)  # 10

del a.score
a.score = -1
print(a.score)  # 'Student' object has no attribute '_score'
